Great Pack, the name you were looking for is "Gnass". National has them in their catalogs.
At my VFD We use the Structural Standpipe Bag, it holds 500 feet of 1 inch hose, Gated Wye, and a nozzle, with no problem.
My work truck should be a type 6 engine, but I've added a bunch of extras. With 2,100 feet of hose, Nozzles, Wyes, Tees, and similar stuff, I move from initial attack right into mopup, and am often the only forestry unit needed for mopup, with the VFDs supplying a Tanker and some people.
here's one way to accordian in a backpack
This works for a progressive hose lay.
Lay out your 1.5" hose, attach your 1.5" gated wye to the end, then connect your 1" to the wye (via a 1.5" - 1" reducer). Holding the nozzle on the 1" at the wye, stretch your 1" line along/on top of the 1.5". Then you suck out as much air as possible using a Mark III hand primer, or any other way you can. When hoses are flat, tape them together in about 8-10 spots with a wrap or two of masking tape (or you can use flagging and tie the hoses together) or other similar tape (it has to something that will tear when the hoses are charged, so glass/fiber tape is a no-no). NOW, start with the gated wye in the bottom of the pack (works better if the wye is shut on both sides), and accordian it in as best you can, leaving a small tail sticking out of the bag to grab to hook-up. Close flap and buckle. Leave shoulder straps as wide as possible to make donning the pack easier.
This method works well in the green nylon backpacks the feds have like this one
Another form of the Gasner
This one is nice in that there is nothing extra to carry or pick up later. When the 1.5 runs out, you drop the remining bit on your back, pull the strings holding the 1" together and charge it. One disadvantage is that the 1" can kink from twists a little easier being in a coil, rather than laid out straight.